1. Field of the Invention
The present invention relates to electromagnetic energy sources for optical detection systems, more specifically, to multi-light-source optical input devices.
2. Description of the Related Art
Displacement detection based on optical technology is used in several applications, including optical input devices for computer systems. Data processing systems, or computer systems generally, are used in conjunction with a variety of input devices, such as for example, keyboards, pointing devices (e.g., mice, touchpads, and trackballs), joysticks, digital pens, and the like. FIG. (“FIG.”) 1 shows a sample diagram of a conventional computer system 100 including two input devices, a pointing device 110 and a keyboard 140. One example of optical displacement detection technology used in a pointing device is an optical mouse. Examples pointing devices using optical detection technology and their operation are described in U.S. Pat. No. 5,288,993 to Bidiville, et al. (issued Feb. 22, 1994) entitled “Cursor Pointing Device Utilizing a Photodetector Array with Target Ball Having Randomly Distributed Speckles” and U.S. Pat. No. 5,703,356 to Bidiville, et al. (issued on Dec. 30, 1997) entitled “Pointing Device Utilizing a Photodetector Array,” the relevant portions of which are incorporated herein by reference in their entirety.
There are significant advantages to using optical input devices over other types of input devices, such as, mechanical or opto-mechanical input devices. For example, mechanical or opto-mechanical input devices have mechanical components that are more susceptible to breakdown, wear out, or clogging. Optical input devices reduce, and in some instances eliminate, a number of mechanical parts susceptible to these problems. Instead, optical input devices are manufactured with solid-state components that are less susceptible to such breakdown, dirt, or wear out.
Optical displacement detection systems use differences in images captured over short periods of time to detect displacement and derive movement of a device relative to a surface. In general, a first image of a surface is captured at a first time and is compared with a second image captured shortly after the first image. The changes in the images over a small period of time correspond to displacement of the systems with respect to features of the surface. This displacement information is processed to derive movement data, such as, movement associated with a user display. For example, an optical pointing device in the form of a mouse captures images of a desk surface, and in the case of trackball, of a ball, providing displacement data of features on the surface that is processed to derive movement of a cursor in a computer screen.
FIG. 2 illustrates a conventional optical displacement detection system 200. The conventional optical displacement detection system 200, or optical system in general, includes a conventional illumination subsystem 210 and a conventional optical sensor or detection subsystem 220. The conventional illumination subsystem 210 includes a conventional illumination lens 230 and a conventional source of electromagnetic energy or light source 250. Typically, the light source 250 is a type of light emitting diode (“LED”), for example, a conventional red LED, a laser diode, or the like. Generally, the light source 250 is attached to a printed circuit board (“PCB”) (not shown) and positioned with respect to the illumination lens 230 to direct light to an illumination spot 201 on a working or tracking surface 205 (e.g., a desk surface, pad, ball, or the like).
A conventional sensor subsystem 220 includes an imaging lens 240 and a sensor 260. The sensor 260 typically includes an image-capturing module 261, for example, one or more photosensor arrays. Some sensors 260 also include controller circuitry 262 associated with the image-capturing module 261, for example, in the form of digital circuits in the same die or device package. Generally, the controller circuitry 262 performs digital signal processing (“DSP”) to derive movement data from the captured images. The sensor assembly 220 is also typically mounted on the PCB and positioned so that the imaging lens 240 optimally captures the electromagnetic energy (e.g., light) scattered from surface 205.
The area of surface 205 that scatters electromagnetic energy and is scanned or “imaged” by the sensor at any given time during normal operation is referred to as an imaged area 202. It should be noted that although typically surface 205 is a flat surface, such as a mouse pad, table top, or the like it is not necessarily so. Surface 205 can be any surface, for example, a person's arm or hand, a sphere (as in a track ball pointing device), the arm of a chair or couch, or any other surface that can be placed in close proximity with the optical displacement detection system 200. The sensor analyzes the images scanned or taken of the surface 205 to provide displacement information. Preferably, the imaged area 202 substantially overlaps with the illumination spot 201 so that the light is efficiently used to illuminate only that area of the working surface 205 that is imaged or scanned by the sensor 260. However, due to misalignment and other mechanical tolerances in optical system components, illumination spot 201 is generally larger than the imaged area 202 to guarantee that enough electromagnetic energy is scattered towards the sensor 260.
The performance of an optical displacement detection system 200 depends on several factors. For example, good surface illumination and good image quality are important factors for the efficient performance of an optical input device 110. In addition, the alignment of all the components that contribute to the optical path in an optical detection system 200 is important for the optimal illumination of the imaged area 202, that is, the alignment between lenses, light source, and sensor is important for the optimal overlap of the illumination spot 201 with the imaged area 202 on the working surface 205. Co-pending U.S. patent application Ser. No. 10/122,488, filed Apr. 12, 2002, entitled “Attachment System for Use in an Optical Illumination System,” which is commonly assigned to the assignee of the present invention and is incorporated herein by reference in its entirety, is directed to one embodiment of an improvement in component alignment.
Another performance factor is the quality of the image that reaches the image-capturing module 261. This in part depends on optical filtering of the light by the imaging lens and subsequent processing. For example, improvements in optical filtering and subsequent processing are provided by U.S. Pat. No. 6,256,016 (Jul. 3, 2001) to Piot et al., which is commonly assigned to the assignee of the present invention and is incorporated herein by reference in its entirety.
Similarly, the source of electromagnetic energy for the illumination subsystem 210 directly impacts the performance of the optical displacement detection system 200. One improvement in illumination systems 210, for example, is described in co-pending U.S. patent application Ser. No. 10/033,427 filed Dec. 27, 2001, entitled “An Optical Illumination System and Method,” which is commonly assigned to the assignee of the present invention and is incorporated herein by reference in its entirety, and which is directed to an efficient illumination system that includes specialized lenses.
However, there is a lack of performance improvements directed to features of the illumination subsystems 210. Particularly, illumination subsystems 210 utilizing either coherent or non-coherent light sources. In general, the performance of optical displacement detection systems is mostly affected by several illumination factors or characteristics of the illumination subsystems, in particular, by light wavelength, light beam impinging angle (shown as “α” in FIG. 2 representative of the median of the light beam, e.g., central ray), homogeneity of the light rays, and intensity. These illumination characteristics affect performance differently depending on the surface 205 of operation. Generally, the higher the intensity of the light source 250, the better the system can perform. However, light intensity directly impacts power consumption of the optical system. In systems in which the power supply is limited, e.g., battery operated systems, it is desirable to minimize the power consumption. Consequently, the intensity of the light source 250 must be commensurate with the performance increase it provides. For example, simply including additional light sources 250 to increase the light intensity may lead to an unjustified increase in power consumption without a significant corresponding increase in performance because other factors, e.g., impinging angle a, homogeneity of light, or wavelength, may have a controlling effect on the performance of the optical system 200 on a particular surface 205.
Further, the pointing device market is becoming crowded with offerings from many different manufacturers. Manufacturers not only need to distinguish their products with performance improvements but also with visually appealing designs. For example, some optical mice suppliers sell devices in different ergonomic shapes, colorful plastic enclosures, and even transparent or translucent enclosures that allow light from the light source 250 of the illumination system 210 to shine through. In particular, this type of feature has lead to optical mice users becoming accustomed to determining operational status of the optical mouse by simply looking at the light emanating from the light source 250. For example, if there is no LED light, a user may think that batteries need to be replaced; or if the light is blinking it may mean that the mouse is lifted too far from a surface; or in the case of a wireless optical mouse, the LED light being off may indicate that a switch needs to be turned on or that the wireless link needs to be reestablished. Thus, the light source 250 itself provides information to the user about the system operational status.
Hence, there is a need for improvements in illumination systems, sensors, and pointing devices to (1) increase pointing device performance, (2) prevent adversely affecting power consumption, (3) provide a way for manufacturers to visually distinguish their devices from competitors, and (4) provide visually status information to users.